International Cooperative Study of ELF VLF Electromagnetic Noises

斯坦福大学ELF VLF辐射计是全球8个观测站之一，设在高知大学理学院地球观测站。利用目前获得的数据，我们进行了以下研究。1. 用于分析VLF电磁噪声波形。假设雷电电流波形为a源，采用快速傅立叶拉普拉斯变换方法进行数值计算。这样，我们就合理地解释了观测到的波形。我们还分析了惠斯勒波形，观察并解释了频散和振幅特性。3. 利用观测到的惠斯勒资料，研究了澳大利亚北部磁共轭区发生的闪电特征。我们制作了一台极低频电磁脉冲的自动波形记录仪，并获得了许多有趣的波形，包括在地球电离层空腔的基频8hz处的非常高的Q值振荡。5. 设计了一种宇宙射线阵雨射电发射波形记录仪，并进行了测试测量。6. 利用埋设在地表下的球形天线测量地电位的系统。并对城市地区的电磁噪声进行了详细的调查。7. 我们仔细核对了ELF VLF辐射计的数据，并将它们与地震的发生联系起来，发现电磁噪声与(1)到达天文台的弹性波和(2)震源的发射时间一致。8. 我们获得了电磁屏蔽室中用锤子敲击岩石所发出的电场波形。9. 为了确定最近在四国发生的地震的震中，已经进行了一次全面的调查。

As one of the eight stations on the globe, the Stanford University ELF VLF Radiometer were set at the Earth Observatory, Faculty of Science, Kochi University. Using data obtained so far we have made the following studies. 1. For analysing VLF electromagnetic noise waveforms. we have assumed the lightning current waveform as source a and made numerical calculations using the Fast Fourie Laplace Transform method. We have thus reasonably interpreted the observed waveforms.2. We have also analysed Whistler waveforms observed and interpreted the frequency dispersion and the amplitude characteristics. 3. And we have studied lightning characteristics which occurred at the magnetic conjugate areas in the northern part of Australia using the observed whistler data.4. We have made an automatic waveform recorder of ELF electromagnetic pulses and obtained many interesting waveforms including a very high Q value oscillations at 8 Hz which is the fundamental frequency in the earth-ionosphere cavity. 5. We have designed a waveform recorder of radio emission which will be emitted from cosmic ray showers, and made a test measurement. 6. The measuring system of the earth potential using ball antennas which are set under the ground surface. and made a detailed surveys of EM noises in the urban area. 7. We have carefully checked the ELF VLF Radiometer data and correlate them with the occurrence of earthquakes and found the EM noises which coincide (1) with the elastic wave arrival at the Observatory, and (2) with the emission time at the hypocenter. 8. We have obtained the electric field waveforms emitted from the rocks hit with a hammer in the EM shielded room. 9. A comprehensive survey has been made to locate the epicenters of the earthquakes which occurred recently in Shikoku.